1. Field
This invention relates to disk drives and, more particularly, to electrical power supplied to disk drive circuitry.
2. Description of the Related Art
Magnetic disk drives are conventionally designed to store large volumes of data on a plurality of disks mounted on a spindle assembly. In general, each disk includes two disk surfaces capable of storing data. On each disk surface, user data is divided into groups of sectors and stored in concentric circular tracks located between an outside diameter and inside diameter of the disk. Embedded servo information is recorded in servo sectors located in radially continuous narrow wedges along the disk surface.
In order to maximize the data recorded on each disk surface, it is desirable to use zone recording techniques. According to such techniques, the rate or frequency at which data is written to a disk surface increases from the inner tracks to the outer tracks to compensate for the fact that data tracks towards the inside diameter of the disk surface are shorter and can hold less data than tracks near the outside diameter. Thus, a relatively uniform data density may be achieved over the disk surface.
Although the recording rate could theoretically be optimized for each track, zone recording techniques typically utilize a relatively low number of discrete recording frequencies. Accordingly, groups of adjacent tracks may be assigned to an array of zones between the innermost track and the outermost track of the disk surface. For example, there may be ten to 20 zones across a disk surface. Data may then be written at the same recording frequency within each zone, and the recording frequency may increase from the inner zones to the outer zones.
In many disk drive applications, including mobile applications, power conservation is critical. To reduce the power needs of the spindle motor, for example, the prior art discloses disk drives designed to rotate at lower speeds in low-power environments. Thus, these prior art disk drives can rotate at a higher speed when the host computing device is coupled to a wall socket (a relatively abundant source of power), and at a lower speed in a mobile, battery-powered mode.
Operation of a disk drive at multiple speeds, however, has a number of drawbacks. First, the performance of a disk drive at lower speeds is significantly impaired, reducing the utility of the mobile mode. Second, there is the difficulty of maintaining a constant fly-height at different speeds. Finally, operating a disk drive at different speeds presents complex electrical engineering issues. For example, the disk drive must be able to read data that was written at a different speed.
There is therefore a need in the art for power conservation measures that may be efficiently implemented in disk drives.